Peak voltage on the incoming wave form to a rectifier in a wireless device (e.g., an RFID tag) is approximately 2× higher than the DC voltage that comes out of the rectifier. The gate oxide of the rectifier transistors is subjected to this high voltage, while the rest of the circuit is not. Thus, rectifier circuits having single diode-wired transistor circuits are subject to potential gate oxide breakdown problems in the single diode-wired circuits.
One approach to avoiding potential oxide breakdown problems is to increase the oxide thickness. However, a thicker oxide generally reduces the performance of transistors in the internal circuits that have the same oxide (or that have an oxide formed in the same processing steps).
This problem can also be addressed by forming oxides of different thicknesses in each type of device (e.g., rectifier transistor vs. logic transistor). However, this adds significant process complexity and cost to the process. A thicker gate oxide in the rectifier transistors also reduces the rectifier efficiency, due to reduced transistor turn on characteristics.
In addition, the dielectric layer of a tuning capacitor(s) (e.g., a tank capacitor in power harvest or conversion circuit) sees a higher voltage than the rectified voltage that the transistors see. To get similar reliability, typically one would use a thicker insulator for the tank capacitor. This generally means extra processing steps, as discussed above.
To reduce the cost of wireless devices such as RFID tags, efforts have been made to explore printing as a low-cost, high-throughput technique for forming certain films for such devices. However, the purity of the materials is in some cases not as high as the materials used in more conventional integrated circuit processing (e.g., films made by chemical and/or physical vapor deposition onto a single-crystal silicon wafer or a material thereon, followed by photolithography and etching), nor do the films formed using printing necessarily have the same electrical properties and characteristics as films made by more conventional integrated circuit processing. As a result, processing steps that adversely affect transistor performance are even more likely to adversely affect performance of a transistor made using a printing technique, and requiring extra processing steps is likely to adversely affect certain advantages of printing over more conventional photolithography and etching (e.g., lower cost and higher throughput).